Drainage system

ABSTRACT

A drainage system for multi-floor buildings capable of utilizing a single vertical sanitary drainage stack to which lateral floor drainage lines are connected. Plumbing fixtures are connected through trap units to the lateral lines, and liquid seals within the trap units are protected by placing velocity breaking fittings in the vertical stack. The fittings break the velocity of the descending column of waste liquid, thereby preventing development of adverse pressure conditions in the system.

United States Patent 1191 Gorman Dec. 10, 1974 DRAINAGE SYSTEM 1,747,514 2/1930 Kennedy 285/156 x 2,065,523 12/1936 Grocn' er 285/154 1751 Invent: coma, wqodlandi 3,346,887 10/1967 Somme r 4/211 [73] Assignee: Cast Iron Soil Pipe Institute,

Washington, DC. Primary ExaminerHenry T. Klinksiek [22] Filed Sept 24 1973 Attorney, Agent, or Firm-Browning & Bushman l A l. N 1. 1 PP 0 399,953 r 57 ABSTRACT Related Apphcauon Data A drainage system for multi-floor buildings capable of [63] C f S N 152 562 J 14 1971 i g 'f 0 utilizing a single vertical sanitary drainage stack to a an one which lateral floor drainage lines are connected. Plumbing fixtures are connected through trap units to [2%] 1376522215933 the lateral ms, and liquid Seals within the trap units [58] .ld 137/357 are protected by placing Velocity breaking fittings in 1 1 o earc 4/211 the vertical stack. The fittings break the velocity of the descending column of waste liquid, thereby .pre- 5 References Cited venting development of adverse pressure conditions in the system.

15 Claims, 3 Drawing Figures DRAINAGE SYSTEM BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates generally to sanitary drainage systems for multi-floor buildings, and more particularly to an improved system which may employ a single vertical sanitary drainage stack without separate vent piping, wherein the individual liquid trap seals are protected by a unique stack fitting.

.Sanitary drainage systems for multifloor buildings usually include a vertical sanitary drainage stack of pipes, through which liquid wastes, mixed at times with solids, fall substantially vertically to a building sanitary sewerage line that runs horizontally with a slight slope to a public sanitary sewer. The drainage stack is connected at each floor to one or more lateral drainage lines that service the plumbing fixtures located on that floor, each fixture being connected to its associated lateral drain line through a trap unit which is usually located as close as practical to the fixture.

The trapunit is generally U-shaped, and is designed to retain in the bend portion a part of the liquid that flows therethrough, such trapped liquid forming a liquid seal that prevents sewer gases and odors from the vertical drainage stack entering the building through the plumbing fixture.' The depth of the liquid trap seal is usually about "2 inches, and the maintenance of at least a 1 inch seal is usually the minimum acceptable standard.

When large volumes of liquid, such as occur upon the simultaneousflushing of several toilets, are discharged into a conventional vertical drain stack, the high velocities characteristic of bodies in free fall are achieved. These high velocities create an imbalance of pressure within the drainage system. Negative or below atmospheric pressures develop above the volume of falling water,and positive or above atmospheric pressures develop below the volume of water when a fixture is flushed or emptied. Either of these pressures can be more than sufficient to force or break the liquid trap seals of the systems plumbing fixtures, thus enabling sewer gases to enter the building.

2. Description of the Prior Art The method commonly employed to reduce these pressures to safe operating levels is to provide a separate vent piping arrangement for the system. Each plumbing fixture has its trap vented, either independently to the atmosphere outside the building, or to a rate vent stack, of special aerating fittings to connect the lateral lines to the vertical stack. These fittings are of the type shown in US. Pat. No. 3,346,887 to Sommet and are used in place of the conventional Y or T fitting.

While systems incorporating these fittings have shown some success, even better trap seal protection is desirable particularly in view of the increasing demandfor multi-floor buildings which must have plumbing systerns capable of withstanding simultaneous and/or sequential flushing of fixtures without trap seal loss.

Other disadvantages of the system disclosed in US. Pat. No. 3,346,887 include the fact that the system requires, in addition to the aerating fittings, a deaerating fitting located at the bottom of the drainage stack, and the fact that both the aerating and the deaerating fittings are relatively expensive to manufacture.

There is need for an economical sanitary drainage 0 system for use with multi-floor buildings, which may employ but a single drainage stack and which makes use to the greatest extent possible of conventionally available pipes and fittings. The present invention is directed toward satisfying that need.

SUMMARY OF THE INVENTION The present invention provides a drainage system which may be a single stack system and which utilizes commonly available and/or easily fabricated elements. The system of the present invention is more effective than the system of US. Pat. No. 3,346,887 both in reducing trap seal loss and in reducing pressure excursions in the system.

A velocity breaking fitting comprises a part of the invention. According to the present system, the development of adverse positive and negative pressure conditions in the single vertical drainage stack are avoided by reducing the velocity of the falling liquid waste in the stack, through use of the instant fitting. By thus reducing liquid waste velocity it has beenfound that the liquid traps of a sanitary drainage system can be protected, without the use of a separate vent stack system.

A- sanitary drainage system according to the invention includes a series of connected vertical drain pipes that form a vertical drainage stack extending for several or all the floors of a multi-story building. Conventional 45 Ys or sanitary T's are located in the drainage stack at the various floors on which plumbing fixtures are located, for connecting to the stack generally horizontal drain lines that serve the plumbing fixtures on those floors. Each plumbing fixture is connected to its horizontal drain line through a generally U-shaped trap, the lower end of the vertical stack is connected to a building sewer that leads to the public sewer line, and the upperend of the stack is vented to the atmosphere.

In an ordinary substantially vertical drain stack, the

waste liquid together with whatever might be entrained with it accelerates as it falls downwardly reaching a high velocity under conditions of substantially free fall. If the system were unvented, this would create large negative pressures in the upper floors of the building, and large positive pressures at the lower floors, such adverse pressure conditions frequently becoming sufficiently severe to destroy the liquid trap seals associated with the various plumbing fixtures, resulting in the escape of sewer gases and odors into the building through such fixtures.

To prevent such adverse pressure conditions from occurring in an unvented single stack drainage system according to the invention, velocity breaking fittings are employed in the vertical drainage stack, preferably one fitting for each floor level below the uppermost lateral drainage line. The fitting preferably has the same inner diameter as the vertical drain stack, and includes an offset section that is preferably displaced at least one full diameter from the vertical stack, to ensure that it will completely intercept all of the waste liquid and entrained matter. The fitting is also designed to prevent excessive retardation of water which would form plugs. Such water plugs can create essentially the same type of pressure problems as rapidly accelerating masses of water as they flow down the stack without allowing countercurrent air flow to equalize the pressures.

In accordance withthe invention, the falling waste liquid has its free fall interrupted by the velocity break-. ing fittings. Consequently, the liquid wastes have no opportunity to accelerate to a very high velocity, and the creation of adverse pressure conditions is avoided. The present velocity breaking fitting has proven effective to reduce waste liquid velocities by 40 to 50 percent from those normally found in a conventional two-pipe drainage system, whereby pressure conditions within the vertical drainage stack have been held within acceptable limits that ensure against breaking of the liquid trap seals.

Several factors have been found to bear on the effectiveness of the system. For example the placement of the fittings in the stack is an important aspect of the invention. The velocity breaking fittings are spaced apart by generally the nominal distance between floor levels of the building, not to exceed fifteen feet, the lowermost fitting preferably being within fifteen feet of the base of bottom of the stack. Each lateral line may be considered to be associated with the respective velocity breaking fitting closest thereto. It has been found that an offset section, a portion of which forms a circular arc.

Other objects and many of the attendant advantages of the invention will become readily apparent from the following Description of the Preferred Embodiment, when taken together with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1, a multi-story building is indicated generally at 2,'and includes a plurality of floors 4 on each of which is installed one or more plumbing fixtures 6. The fixtures 6 can be of any type and of any number, though for purposes of illustration only one by placing the velocity breakings fittings which are associated with lateral lineswithin a preferred range of distances from their respective lateral lines, the best possible preformance is achieved.

Similarly the configuration of the fitting itself affects the perfonnance of the system. In particular, if the offsetsection has a portion forming a substantially circular arc, the ratio of the radius of curvature of that portion of the fitting to the inner diamter of the fitting is important. If this radius is too small relative to the inner diameter of the fitting, excessive retardation of the falling waste can occur and this in turn can cause plug flow as described above. On the other hand if the radius is too large relative to the inner diameter of the fitting, the fitting may not sufficiently reduce the velocity of the falling waste. In accord with the invention, a preferred range of ratios of the radius of curvature of the offset section to the inner diameter has been found which produces the best possible performance of the fitting.

It is a principal object of the present invention to provide a drainage system which may be of the single stack type, which can be easily and economically installed, and which will assure the maintenance of the integrity of liquid trap seals of the system.

A further object is to provide a single stack system which does not require a special deaerating fitting at the base of the stack.

Another object is to provide a system that utilizes conventional plumbing connections and pipes to the maximum extent.

A further object of the invention is to provide a drainage system having velocity breaking fittings installed in the vertical drainage stack.

One further object of the invention is to provide a drainage system having a velocity breaking fitting with sink is shown on each floor.

Extending vertically upwardly through the building 2 is a vertical drainage stack 8, made of conventional long and short drain pipes 10 and 12 connected in series with conventional branch fittings 14 located at each floor 4 for connection of lateral drain lines 16 thereto. The vertical drainage stack 8 is of substantially uniform inner diameter. The upper end of the stack 8 is vented to the atmosphere (not shown), and the lower end thereof is connected through conventional terminal fittings 18 to a building sewer line 20, which in turn leads to the public sewer (not shown). Each of the plumbing fixtures 6 is connected to one of the lateral drain lines 16 through a generally U-shaped trap unit 22, designed to contain a liquid seal of a few inches in height that effectively prevents sewer gases and odors from the drainage stack 8 entering the building 2 through the plumbing fixtures 6.

The opposite ends of the pipes 10 and 12 have connector flanges 24 and 26 thereon, respectively, and connected therebetween are velocity breaking fittings 28. The fittings 28 preferably each have an inner diameter corresponding to that of the pipes 10 and 12, and include a body 30 having connector. flanges 32 on its opposite ends that are connected by bolts 34 to the flanges 24 and 26, a suitable gasket 36 being clamped between the confronting flanges. Obviously, connector means other than bolted flanges can be used, if desired.

The fitting body 30 includes an upper cylindrical inlet section 38 and a lower cylindrical exit section 40, both aligned on the axis A of the vertical drainage stack 8. The inlet and exit sections 38 and 40 are connected by an intermediate, laterally offset section 42 that is preferably smoothly curved in a manner to be described more fully below.

Several factors bear upon the effectiveness of the system. One of these is the location of the velocity breaking fitting in the stack. In a building such as the one shown wherein a lateral line 16 is located on each floor, the fittings 28 are disposed between adjacent pairs of lateral drain lines 16. In any event the fittings 28 are placed below the uppermost lateral drain line 16 building being spaced apart by feet and the lower 40 feet of the building being occupied by a single highceiling storage floor. Or there may be a floor every 10 feet with some of these floors not having fixtures and lateral lines. Then velocity breaking fittings would be installed along the vertical stack of the building, beginning below the uppermost lateral drainage line, approximately every l0 feet. Of course, slight variations in the spacing of about 3 feet or less could be made.

Each of the lateral lines 16 may be considered to be associated with that fitting 28 which is closest thereto. For example, in the system shown in FIG. 1 each of the fittings 28 may be considered to be associated with the lateral drain line 16 immediately below it. Experiments have shown that the best results are obtained if those fittings 28 which are associated with lateral lines are each placed at a distance of four to seven times the inner diameter of the stack 8 above the associated lateral line 16, or five to 1 1 times said diameter below the associated lateral line and that the fittings 28 should be placed within this range. It should be understood that this distance is measured from the center'of the lateral line 16 at the point where it enters the stack 8, represented by the line N, to' the part of the offset section 42 of the fitting which is farthest from the axis A, represented by the line M. Additionally, it has been found that, while the fittings 28 may be located either above or below their respective associated lateral lines 16, it is preferable to have all the fittings 28 spaced from their associated lateral lines 16 in the same longitudinal direction. In other words, it is best to have the fittings which have associated lateral lines all located above their respective associated lines or all located below the associated lateral lines. Any fitting 28 which is not asso-' ciated with a lateral line 16, due for example to the fact that some floors of the building in question have no lateral lines, should be spaced from the immediately adjacent fittings by a distancegenerally equal to the nominal distance between floor levels but not to exceed fifteen feet. In any event, it will be appreciated that it is unnecessary to place a velocity breaking fitting'above the uppermost lateral line in the building, and in some cases, unnecessary to place a velocity breaking fitting below the first lateral line at the bottom of the building. However it is preferable to have the lowermost fitting 28 located within fifteen feet of the base or bottom of the stack.

Other factors controlling the effectiveness of the system involve the design of the velocity breaking fitting itself.

For example, the centerline CL of the intermediate offset section should preferably be offset from the axis A of the vertical drainage stack 8 by a distance at least equal to one full inner diameter of the pipe 10 thereabove, so that a complete interception of the liquid wastes will occur at each fitting 28, as indicated by the broken lines F in FIG. 2. However it should not be offset so far that'it causes excessive retardation of flow, a

problem which will be discussed in greater detail below.

Another factor to be considered is the angles at which the top and bottom of the offset section 42 depend from the upper section 38 and the lower section 40 respectively. These may be considered to be the smaller of the angles generally defined by the axis A and the centerline CL. Angles of about 45, as shown in FIG. 2, have proven practical and effective in providing sufficient velocity breaking without excessive retardation. However it will be appreciated that the angles can be varied in accord with variations in the amount of offsetting, discussed above, and the radius of curvature, to be discussed below.

It is highly preferably that the offset section be smoothly curved, and in particular, that a major portion of the offset section generally forms a circular arc. Referring to FIG. 2, it will be seen that a major portion of the centerline CL of the offset section forms a circular arc. The ratio of the radius of curvature of this portion of the offset section to the inner diameter of the fitting has been found to be an important factor in the performance of the system of the invention. Experiments have shown that the radius of curvature should be greater than the inner diameter of the fitting and less than 2.5 times this inner diameter.

It has been found that by use of the system of the invention the velocity of the falling waste liquid in a single stack type drainage stack can be reduced by from about 40 to 50 percent over free fall conditions and that the pressures all along the height of the multi-story vertical drainage stack are held to within acceptable limits. Such relatively stable pressure conditions guard against complete destruction of liquid seals in the traps 22, and instead insure that a seal of at least minimum depth, say about 1 to 2 inches, will be maintained.

At the same time, it must be remembered that too excessive a reduction in the velocity of the liquid will also result in pressure problems. For example, if the flow of a first mass of liquid is'excessively impeded by the velocity breaking fitting, a second mass of liquid can catch up with it causing buildup of liquid at that point in the stack. When these masses of liquid finally begin to flow, they may take the form of a non-porous plug of substantially the same diameter as the stack. This type of plug flow does not allow countercurrent air flow in the stack and thus is capable of producing the same extreme positive and/or negative pressures that the invention is designed to eliminate. Therefore, while the fitting is designed to reduce the velocity of the liquid, care must be taken to avoid excessive impedence of the flow.

The factors of fitting design discussed above, i.e. amount of offsetting, angles between the offset section and the upper and lower sections, and ratio of the radius of curvature of the arcuate portion of the offset section to the inner diameter of the fitting all contribute to the proper balance between sufficient velocity breaking and excessive impedence of flow. Several other features of the fitting contribute to this balance. The fitting is of uniform internal diameter substantially equal to that of the pipes 10 and 12 in the stack-Thus there are no restrictions which might encourage compaction of the liquid into a plug. The design of the fitting also allows for complete interception of the stream of falling liquid, yet assures that the curve through which the liquid passes is smooth and shallow. The offset section has a significant vertical component of direction throughout its length. The curve of the fitting is smooth, having no sharp corners. It will also be appreciated that even though section 42 is offset more than one full pipe diameter, the curve thereof is shallow. This is possible because the length of the offset section 42 is relatively great compared to the inner diameter of the fitting and the pipes in the stack. As shown in FIG. 2 this length is about four times the diameter. All of these features contribute to the avoidance'of excessive impedence of flow.

When a conventional toilet is flushed, a substantial flow of water and waste is delivered in a short period of time into the associated lateral drainage line 16. For example, a conventional toilet tank contains 3.5 gallons of water, and will empty in 6.5 to 7 seconds, giving a flow rate of about'30 gallons per minute. If two, three or more fixtures are emptied at about the same time, these flows are rapidly multiplied. It is thus evident that substantial flows can be present in the vertical drainage stack 8, flows which in the absence of the selfcontained, economical and easily installed fixtures 28 or a separate vent stack can cause severe pressure fluctuations in the drainage system.

The curves of FIG. 3 were derived experimentally, utilizing an installation of 4 inch pipe on a tower simulating a story building, with 99 fixture units connected to lateral drain pipes though trap units, the installation being of the single stack type. Curve I shows the pressures in such a drainage system equipped with one of the velocity breaking fittings 28 installed above each lateral ine, resulting when three toilets, one each on the 4th, 5th, and 6th floor levels were flushed simultaneously into the vertical drainage stack, giving a flow of about 90 to 100 gallons per minute. The resultant pressure conditions caused a maximum liquid trap seal loss of about 1/8 inch, which is negligible. Curve II shows pressure conditions for the same system, when six toilets, one each on the 4th, 5th, 6th, 7th, 8th and 9th floors were flushed simultaneously, which is considered to be a load beyond what might normally occur, In this case, an acceptable maximum liquid trap seal loss of 7/16 inch occurred, the nationally recognized criteria for trap seal loss being a maximum of 1 inch depth of liquid from a trap.

Curve III shows the results with the same system, without the use of the fittings 28. The same load was created as for Curve I, but here pressure variations in the vertical drainage stack were recorded as high as inches of water column above and below atmospheric pressure, which pressure conditions emptied all of the liquid seal traps connected to the system. It should be noted that the horizontal scales for Curves I and II in FIG. 3 are much greater than the scale for Curve'III.

The test results as shown in FIG. 3 clearly establish the success of the present single stack drainage system and method.

Other tests have shown the superiority of the system of the invention over the type of system, with its special aerator and dearating fittings, which is disclosed in US.

Pat. No. 3,346,887. This system is known commercially itary napkins were used. In each test, the trap seal loss was measured in either the trap of the water closet or the trap of the lavatory. These losses were expressed in terms of relative, or percentage of, trap seal retention. This can be easily converted to trap seal loss in inches if the depth of the original trap seal is known.

At this point it should be noted that the traps used in the above-described tests on the Sovent system were European standard traps which had a depth of 2 %in. In a trap of this depth, an inch of water could be lost without destruction or failure of the seal. However in the United States the minimum trap depth allowed, and that which is ordinarily used, is 2 in. A loss of 1 inch of water from a trap of this depth is considered a failure of the seal. Thus while the results of most of the tests on the Sovent system were considered successful in terms of European standards, many of them would be considered failures or near failures in terms of the more critical U.S. standards.

For example in test No. 1B? on the Sovent systemin which one water closet on each of floors 107 and one lavatory on floor 10 were flushed simultaneously, a trap seal loss of 1.04 in. was experienced on floor 3. In test No. 1B*,, water closets on each of floors 10-7 and one lavatory on floor 10 were flushed simultaneously with one paper diaper being addedto each of the water closets on floors 10, 9 and 7; a trap seal loss of I07 in. was experiences on floor 5. Each of these would be considered failures in terms of US. standards. In test No. 1B* one water closet on each of floors l0-7 and one lavatory on floor 10 were flushed simultaneously, with sanitary napkins and toilet paper being added to the closets on floors l0, 9 and 7; and a seal loss of .99 in. was experienced on floor 5. In test No. lA* one water closet on each of floors 10-8 and one lavatory on floor 10 were flushed simultaneously; a seal loss of .89 occurred on floor 5. Each of these latter two results would be considered near failures or dangerous in terms of the US. standards.

The four tests discussed in detail above were essentially reproduced on a'single stack system, having velocity breaking fittings in accord with the present invention and 2 in. trap seals, in a similar 10 story tower. No deaerating fitting was used at the base of the stack. In order to acquire more complete data, fixtures were installed on every floor, and the trap seal lossin each trap was measured on every test. Using the same flushing combinations and additives as described above, the four tests showed that there were no trap failures, i.e'., losses of I in. or more, in any of the traps in the system. Furthermore, the greatest seal loss experienced in any of the traps in the two tests in which no additives were used was H2 in. while the greatest loss in the two tests using additives was 3/4 in. Both of these values are well within the acceptable range for both US. and European standards.

Others of the tests of the Sovent system, described in the Building Science Series 4l'publication, produced failures and near failures. Many of these tests were substantially reproduced for the system of the invention.

While in these latter tests some procedural differences were necessitated by the fact that the Sovent test tower had two bathrooms on each floor containing fixtures while the tower used to test the invention had one bathroom on each floor, the tests were designed to be as close as possible in procedure to the tests performed on the Sovent system. Additionally the tests were designed to place loads on the system of the invention which were at least as great and sometimes greater than the loads on the Sovent system in the corresponding tests. ln all the tests performed on the system of the invention, there were no failures in any of the traps, the greatest loss for any test being 3/4 in.

It should be noted at this point that in the Sovent test tower no fixtures were located on floors 4 and 6 and thus no trap seal loss measurements were taken on these floors. However these floors were found to be the most critical in the tests on the system of the invention. Thus in view of the failures and near failures that occurred on floors 3 and 5 of the Sovent system, it is probable that even greater losses would have occurred on floors 4 and 6 had fixtures been installed on these floors.

Another publication, The Single Stack Drainage Systern, US. Department of Housingand Urban Development, Federal Housing Administration, December 1970, described a different test on a Sovent system. In this system a Sovent aerating fitting was placed at each horizontal branch interval in a multi-story building, except for the first floor above which was placed the deareating fitting. Fixtures on floors, 3, 8 and 11 were flushed simultaneously and the negative pressure fluctuations, considered to be most critical as they may represent trap seal losses, reached peaks of approximately =.75 inof water.

As a comparison, a similar test was made using the ten story test tower of the invention described above in regard to the other comparative tests with the Sovent system. Because in the Sovent system last described the deaerating fitting was placed above the first floor of the building, it was considered that this floor was effectively removed from the system and that the second floor was effectively the first floor. Accordingly in the test on the system of the invention, fixtures on floors 10, 7 and 2 were flushed simultaneously and the maximum negative pressure fluctuation recorded was -.2 in.

The above experiments clearly show that a single stack system according to the invention produces excellent performance even exceeding that of the Sovent type system. Yet the system of the invention is much less expensive. It is estimated that the cost of one of the velocity breaking fittings of the invention is about onefifth that of one of the special aerator fittings of the Sovent system. Furthermore the system of the invention requires less space. It also provides greater flexibility because the velocity breaking fittings may be disposed at a number of possible positions in the stack.

Returningto FIG. 1, depending upon the results desired and local code standards, one of the fittings 28, can also be installed above the terminal fittings 18, if desired. It is evident that the method and system of the present invention make it practical to construct a single-stack drainage system using all conventional components, except for the velocity breaking fitting 28, a system that will effectively function to preserve liquid trap seals. Or if desired, a suitable multi-piece velocity breaking fitting may be formed of conventional bends" and could in at least some instances be used in place of the integral fitting 28.

The fittings 28 are preferably located just below the connections of the lateral drainage lines 16 to the vertical stack 8, but they can also be positioned elsewhere along the stack as specified above, eg just above such juncture. However, by positioning them just below the juncture, flow in the stack at the juncture is reduced in velocity to the maximum extent, thereby assuring minimum impact on trap seals in communication with the lateral line 16.

While the invention has been described in relation to a multi-floor building, it could be used for example in a two story building in which case the velocity breaking fitting would be placed between the two floors.

It will also be appreciated that while, in the system shown, there is only one lateral line for any given floor level, the invention could be used in a system having several lateral lines entering the stack at one level as is well known in the art.

Obviously, many modifications and variations of the present invention are possible.

I claim:

.1. A sanitary drainage system for a multi-floor building, comprising: a substantially vertical sewerage drainage stack extending upwardly within said building, at least one lateral sewerage drainage line connected to said vertical drainage stack, said lateral drainage line being connected to a plumbing fixture through a trap unit for containing a liquid trap seal; and a plurality of fittings installed in said vertical stack and being spaced apart by a distance generally equal to the nominal distance between floor levels of said building, but no greater than 15 feet, the lowermost one of said fittings being within 15 feet of the base of the vertical drainage stack, and said lateral drainage line being associated with the closest one of said fittings, each of said fittings comprising: an upper inlet section connected to said vertical stack and having a singlefitting inlet substantially in alignment with the axis of said vertical stack; an intermediate offset section connected to the lower end of said inlet section and offset from said axis, and a lower exit section connecting said offset section to said vertical stack, the lower end of said exit section being in alignment with said axis, each of said fittings having a longitudinal centerline lying in a plane.

2. A drainage system according to claim 1 wherein said offset section has a portion, said longitudinal centerline at said portion defining a circular arc.

3. A drainage system according to claim 2 wherein the radius of curvature of said longitudinal centerline at said portion is greater than the inner diameter of said fitting and less than 2.5 times the inner diameter of said fitting.

4. A drainage system according to claim 3 wherein said stack and said fitting are of substantially constant inner diameter. i

5. A drainage system according to claim 3 wherein said offset section is connected to said inlet section and said exit section through respective approximately 45 angles.

6. A drainage system according to claim 1 further comprising a plurality of said lateral drainage lines, each of said lateral drainage lines having associated therewith a respective one of said fittings.

7. A drainage system according to claim 6 wherein said fittings associated with said lateral drainage lines are spaced from their respective associated lateral drainage lines along said vertical drainage stack by a distance of four to seven times the inner diameter of said vertical drainage stack above their respective associated lateral drainage lines or by a distance of five to 11 times said diameter below their respective associated lateral drainage lines.

8. A drainage system according to claim 7 wherein said offset section has a portion, said longitudinal centerline at said portion defining a circular arc.

9. A drainage system according to claim 8 wherein the radius of curvature of said longitudinal centerline at said portion is greater than the inner diameter of said fitting and less than 2.5 times the inner diameter of said fitting.

10. A drainage system according to claim 7 wherein the inner diameter of said stack and the inner diameter of said fitting are substantially equal.

11. A drainage system according to claim 1 wherein said system is a single stack system.

12. A drainage system according to claim 1 wherein said offset section is offset at least one inner diameter of said stack.

13. A drainage system according to claim 1 wherein said fitting has smooth uninterrupted inner wall surfaces.

14. A drainage system according to claim 1 wherein said inlet section is connected to said offset section through approximately a 45 angle. 1

15. A drainage system according to claim 1 wherein said lower exit section is connected to said offset section through approximately a 45 angle.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,853,1 l0 Dated December 10, 197 i Inventor( s) John P. Gorman It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In column 9, lin 35, delete and substitute therefor the symbol Signed and sealed this 11th day of March 1975.

(SEAL) Attest' c. MARSHALL DANN I RUTH C. MASON c Commissioner of Patents I and Trademarks Attesting Officer 

1. A sanitary drainage system for a multi-floor building, comprising: a substantially vertical sewerage drainage stack extending upwardly within said building, at least one lateral sewerage drainage line connected to said vertical drainage stack, said lateral drainage line being connected to a plumbing fixture through a trap unit for containing a liquid trap seal; and a plurality of fittings installed in said vertical stack and being spaced apart by a distance generally equal to the nominal distance between floor levels of said building, but no greater than 15 feet, the lowermost one of said fittings being within 15 feet of the base of the vertical drainage stack, and said lateral drainage line being associated with the closest one of said fittings, each of said fittings comprising: an upper inlet section connected to said vertical stack and having a single fitting inlet substantially in alignment with the axis of said vertical stack; an intermediate offset section connected to the lower end of said inlet section and offset from said axis, and a lower exit section connecting said offset section to said vertical stack, the lower end of said exit section being in alignment with said axis, each of said fittings having a longitudinal centerline lying in a plane.
 2. A drainage system according to claim 1 wherein said offset section has a portion, said longitudinal centerline at said portion defining a circular arc.
 3. A drainage system according to claim 2 wherein the radius of curvature of said longitudinal centerline at said portion is greater than the inner diameter of said fitting and less than 2.5 times the inner diameter of said fitting.
 4. A drainage system according to claim 3 wherein said stack and said fitting are of substantially constant inner diameter.
 5. A drainage system according to claim 3 wherein said offset section is connecteD to said inlet section and said exit section through respective approximately 45* angles.
 6. A drainage system according to claim 1 further comprising a plurality of said lateral drainage lines, each of said lateral drainage lines having associated therewith a respective one of said fittings.
 7. A drainage system according to claim 6 wherein said fittings associated with said lateral drainage lines are spaced from their respective associated lateral drainage lines along said vertical drainage stack by a distance of four to seven times the inner diameter of said vertical drainage stack above their respective associated lateral drainage lines or by a distance of five to 11 times said diameter below their respective associated lateral drainage lines.
 8. A drainage system according to claim 7 wherein said offset section has a portion, said longitudinal centerline at said portion defining a circular arc.
 9. A drainage system according to claim 8 wherein the radius of curvature of said longitudinal centerline at said portion is greater than the inner diameter of said fitting and less than 2.5 times the inner diameter of said fitting.
 10. A drainage system according to claim 7 wherein the inner diameter of said stack and the inner diameter of said fitting are substantially equal.
 11. A drainage system according to claim 1 wherein said system is a single stack system.
 12. A drainage system according to claim 1 wherein said offset section is offset at least one inner diameter of said stack.
 13. A drainage system according to claim 1 wherein said fitting has smooth uninterrupted inner wall surfaces.
 14. A drainage system according to claim 1 wherein said inlet section is connected to said offset section through approximately a 45* angle.
 15. A drainage system according to claim 1 wherein said lower exit section is connected to said offset section through approximately a 45* angle. 